1. Field of the Invention
The present invention relates to a camshaft support structure for an internal combustion engine, and specifically to a camshaft support structure suitable for application to an internal combustion engine mounted in a vehicle.
2. Description of the Related Art
Japanese Patent Application Publication No. 7-166956(JP-A-7-166956) describes a head cover that is formed with an integral upper bearing for supporting a camshaft. A camshaft is used in an internal combustion engine to impart lift to an intake valve and an exhaust valve. When the camshaft lifts the intake valve or the exhaust valve, an associated repelling force impels the camshaft in the direction of the head cover. For this reason, the upper bearing supporting the camshaft on the head cover side is required to have a high degree of rigidity.
According to the described structure, because the upper bearing is provided integrally with the head cover, it exhibits a high rigidity. For this reason, it is possible to support the camshaft of the internal combustion engine with sufficient rigidity.
The head cover described above is tightened to the peripheral part of the cylinder head by bolts. The lower bearing that, together with the upper bearing, supports the camshaft is tightened to the head cover and to the cylinder head in a space formed between the head cover and the cylinder head. By adopting a structure such as this, the only location that needs to be sealed in the vicinity of the head cover is the boundary between the head cover and the cylinder head. In the disclosed structure, therefore, it is possible to reduce the risk of oil leakage while imparting high rigidity with respect to the structure supporting the camshaft.
However, because the head cover is only to tightened the cylinder head, the repelling force applied to the camshaft is transmitted only to the head cover and propagated only to the cylinder head. In other words, in the described structure, the repelling force applied to the camshaft is propagated in a concentrated manner in the vicinity of the edge at which the head cover and the cylinder head are tightened. For this reason, in the structure described in JP-A-7-166956, if it is not possible to achieve sufficient rigidity in the head cover, a condition can occur in which it is not possible to impart sufficient rigidity to the part supporting the camshaft.